The weakest points in hydraulic systems are their joints. That is where leaks are most likely to occur. Consequently, much thought has been given to the design and construction of hydraulic joints. This is as true today, as a wide variety of plastics are used to make the pipes and fittings, as it was in the past, when primarily metal and rubber pipe were used in hydraulic systems.
Plastic pipes are used today because they are relatively inexpensive and can be designed for a wide variety of applications. PEX and PEX-Al-PEX pipes, for example, were designed for heating systems and are now also used for chemical and sewage transport.
When plastic pipe is used, it is typically pushed over a mating portion of a fitting which is a bit larger in diameter than the inside of the pipe. This causes the pipe to stretch and creates a press-fit which helps to make a leak-proof seal. However, stretching the plastic decreases its wall thickness, thereby weakening that part of the pipe at the joint. To compensate for this inherent weakness, reinforcement sleeves are used to strengthen the joint and make them more leak-proof.
There is shown, for example, in U.S. Pat. No. 4,293,147, to Metcalfe et al., a method for connecting a plastics pipe to a fitting incorporating an externally grooved insert. The insert, which is a tight fit in the pipe, is forced into the end of the pipe, and a sleeve, previously located on the pipe, is then forced to the end of the pipe so that the pipe end is tightly gripped between the insert and the sleeve. The insert is tubular and is provided with a plurality of circumferential grooves in its outer surface. Each groove has in axial section, substantially straight sides and a straight base, the angle between the base and each side being obtuse. Insertion of the insert causes the external diameter of the pipe to increase so as to be greater than the internal diameter of the sleeve. This is a slow manual process which depends upon the manual dexterity and strength of the operator.
Soft flexible plastic pipes can be assembled on fittings manually. Reinforcing sleeves that screw onto the fitting are often employed to simplify assembly.
When relatively hard pipes are needed, manual assembly is time-consuming, as the pipe is difficult to mount over the fitting. In such cases, another step is employed to form a bell-shaped opening at the end of the pipe. In this step, the end of the pipe is forced over a bell-shaped die, which expands the pipe to such an extent that it can be slipped onto the fitting. Once mounted on the fitting, a sleeve is either crimped over the coupling or pushed into place. As this is very time-consuming and requires the application of force, a number of devices have been developed that assist the coupling process. Two examples are as follows.
U.S. Pat. No. 6,050,608, to Hattori et al., describes a fitting for a plastic pipe comprising two parts, that is, a fitting main body and a retaining ring put over the top end of a plastic pipe. A hole is pierced in the circumferential surface of the retaining ring for moving the top end of the plastic pipe, together with the retaining ring, to a flange on the fitting. A plurality of large diameter portions of fitting main body diametrically enlarge the top end portion of the plastic pipe to which the inner core is inserted, and the retaining ring compresses the top end portion of the pipe onto the fitting, thereby preventing the mounted plastic pipe from slipping off. The inherent flaw in this design is the need to pierce, and consequently further weaken, the pipe particularly in the region where it has already been stretched.
U.S. Pat. No. 5,749,604, to Williams, describes a coupling system for copper pipes in which a tapered wall is formed on one of two tubular pipe members for press-fit engagement with a wall of the second pipe member, and the two pipe members are pressed together in an axial direction to bring the tapered wall and the other wall into direct press-fit engagement with each other. The two pipe members can, for example, be a length of copper water pipe and a copper pipe fitting, and in certain disclosed embodiments, the pipe members are drawn together by a tool having axially movable jaws which engage the pipe members and are driven together in the axial direction by an actuator and linkage which move in a perpendicular direction. As this invention was designed to create press-fit couplings in copper pipe, it has no sleeve mounting operation.
Accordingly, there is a long felt need for a method and device which mounts a pipe on a fitting in one smooth operation that includes the assembly of a sleeve and ensures a leak-proof seal without damaging any of the components and in a single operation.